The present invention relates to a method for the preparation of a (meth)acryloxyalkyl group-containing organopolysiloxane of a linear molecular structure or, more particularly, to a method for the preparation of a (meth)acryloxyalkyl group-containing organopolysiloxane of a linear molecular structure by the ring-opening siloxane rearrangement polymerization reaction of a cyclic organopolysiloxane oligomer having (meth)acryloxyalkyl groups bonded to the silicon atoms.
As is well known, (meth)acryloxyalkyl group-containing organopolysiloxane of a linear molecular structure is a useful silicone material, for example, as the principal ingredient in a surface-release coating agent by effecting polymerization at the (meth)acrylic groups. A (meth)acryloxyalkyl group-containing organopolysiloxane of a linear molecular structure is conventionally prepared by the ring-opening siloxane rearrangement polymerization reaction of a cyclic organopolysiloxane oligomer having (meth)acryloxyalkyl groups bonded to the silicon atoms either alone or as a mixture with another cyclic organopolysiloxane oligomer having no (meth)acryloxyalkyl groups in the presence of an acid as a catalyst followed by neutralization of the acidic catalyst with a basic compound. This method of acid-catalyzed polymerization reaction has some problems and disadvantages. For example, neutralization reaction of an acid with a basic compound is necessarily accompanied by the formation of water as a reaction product while water in the (meth)acryloxyalkyl group-containing organopolysiloxane acts as a hydrolyzing agent on the (meth)acrylic ester groups in the presence of an acidic or basic compound so as to cause a decrease in the effective content of the (meth)acryloxyalkyl groups as the functional groups in the organopolysiloxane product. Moreover, the above mentioned hydrolysis reaction of the ester groups eventually leads to the formation of microgels which cause a great decrease in the filtrability of the reaction product due to clogging of the filter paper or cloth when it is subjected to filtration to remove the salt formed by the neutralization reaction and other solid materials.